1. Field of the Invention
The present invention relates generally to spinal surgery and, more particularly, to an electromagnetically guided spinal rod system for the placement of pedicle screws, rods and other types of bone fixation systems.
2. Description of the Prior Art
It can be appreciated that bone screw/rod fixation systems have been in use for years. Typically, bone screw/rod fixation systems designed for spinal surgery are comprised of a number of pedicle screws and rods having a main purpose to secure one or more spinal segments. This technique is used to stabilize the spine across the vertebral levels to which it is applied in order to augment the fusion process. To be operational, most systems require one or more rods to be placed inside openings in the heads of bone screws that have been pre-positioned in the vertebrae. Most fixation systems are positioned after an extensive surgical dissection has stripped the musculature completely off the posterior aspects of the vertebrae involved. After placement of the screws, the rods are inserted via the open operating window. A less common method involves a percutaneous approach such as the one disclosed in U.S. Pat. No. 6,530,929 to Justis et al., in which the rods are passed through a narrow incision (such as, by way of example only, a stab wound) after the pedicle screws have been placed. In this type of system the rod is guided into the screw heads by a mechanical arm attached to the screw inserters.
The main problem with conventional bone screw/rod fixation systems is that the extensive muscular dissections required by the open (as opposed to percutaneous) pedicle screw and rod systems produce potentially severe adverse clinical effects. While there are some newer methods designed to reduce the tissue damage accompanying pedicle screw and rod insertion, most spinal fixation systems require the potentially disabling extensive dissection of the surrounding muscular tissue. One problem associated with conventional percutaneous bone screw/rod fixation systems is that the insertion step is done blindly. Accurate rod placement is completely dependent upon the proper functioning of the mechanical arm that controls the rod and its geometric relationship to the various screw heads.
In the existing percutaneous spinal fixation systems, there are no built-in mechanisms that indicate how closely the rods actually follow their intended paths or more importantly, whether or not the rods reach their proper resting position between the screw heads and the gaps in the screw inserters. Another problem with current percutaneous bone screw/rod fixation systems is that the trajectory or path that the rod takes to its target is completely determined by the geometric parameters of the rod positioning system. Specifically, once the procedure has begun, the operating physician cannot modify the rod insertion trajectory. Due to variations in the anatomical structure of different patients and the particular angles of the screw placements, the capacity to modify the path of the rod once the procedure has begun is a very desirable feature. Furthermore, the reliance of existing percutaneous systems on a “one-path” method of rod placement make such systems extremely sensitive to the position of the pedicle screws if more than two screws per side are used, reducing the available trajectories for pedicle screw placement.
While these devices may be adequate for the particular purpose to which they are addressed, they do not provide the least invasive means possible for the placement of pedicle screws, rods and other types of bone fixation systems. The present invention cures this deficiency by the application of a novel concept governing positioning of the rod.